For a party run for more than four decades on the lines of a near theocracy with an omnipresent "Mullah" at its head there have been unprecedented and heretical mutterings inside the Democratic Unionists over recent months. The unthinkable became suddenly possible and necessary - Paisley would have to go.

First his son Ian Junior had to exit stage left after a series of embarrassing revelations about his links to a North Antrim businessman. Ian Junior departed from his post as a junior minister last month. Once the one-time heir apparent to the Paisley dynasty had gone the signals being transmitted in private from inside the DUP indicated that his father wouldn't be far behind him, albeit they cautioned some time after the summer.

On Valentine's Day Paisley's party received a disturbing 'Dear John' letter from the unionist electorate. The DUP lost the first by-election since the party agreed to share with Sinn Fein following the St Andrews peace deal at the end of 2006. The Ulster Unionists took the council seat in large part because the DUP's support base was split. A sizable 20% of the DUP vote went instead to Traditional Unionist Voice, a new force in unionism which opposes the power sharing arrangement with republicans. Jim Allister, TUV's founder and ex-DUP MEP for Northern Ireland, was quick to emphasise why his old party had suffered a setback.

'What an unhappy St.Valentine's Day for the Chuckle Brothers,' Allister said smirking as the count in Dromore, Co Down drew to a close. He was referring to the remarkable and once unthinkable political double act that has run Northern Ireland since St Andrews - First Minister Paisley and his ever smiling deputy and former IRA chief-of-staff Martin McGuinness. Following Paisley's announcement Allister is no doubt still smirking and enjoying the supreme irony of his estrangement from his former leader. For it was Paisley who brought Allister back into politics just a couple of years as his choice as MEP to replace him in Brussels; it is how Allister who has precipitated Paisley's retirement.

Many in the DUP have regarded the closeness and chumminess of the duo as electorally costly and now want a much more cold-blooded, business-like relationship with Sinn Fein ministers. Reports that Paisley senior may stand down later this year as party leader and First Minister were entirely accurate. Having taken the party to the top of the mountain and led them to the milk-and-honey of power, it now seems the DUP decided the time was right to leave their Moses behind.

Party sources had been briefing about a new leadership replacing the Paisleyite dynasty possibly as early as this autumn. Perhaps with a mind to the fate of one of the many Prime Ministers he has seen off, Margaret Thatcher, Paisley decided to leap before he was pushed off the scene.

He will therefore bow out at an international investment conference fronted by Bill Clinton in Belfast this May.

Finance minister and DUP deputy leader Peter Robinson will in all likelihood replace Paisley as first minister. Meanwhile, according to senior party figures, the DUP leadership may pass over to North Belfast MP and Enterprise Minister Nigel Dodds. The Cambridge educated Everton supporting Dodds represents the DUP's second generation, still in his late 40s but someone who straddles the two wings of the party, both a fundamentalist Christian and, like Robinson, also a pragmatic technocrat.

The Robinson-Dodds DUP dream ticket would also open up the possibility for a radical reshaping of unionist politics. Robinson is known personally to favour the creation of a single super-unionist party. With Paisley now out of the way (a man who historically generated almost as much loathing and mistrust within the more Ulster Unionist Party than among nationalists) a pathway could be cleared leading towards unionist-fusion.

The opening steps towards a single unionist movement would take place before the next British general election. In at least two constituencies - Fermanagh and South Tyrone and South Belfast - unionism could claw back seats lost to nationalists (respectively Sinn Fein and the SDLP) if there was one agreed unionist candidate. If such an electoral pact could be formed and yield unionism two extra seats, and with them further clout in a possible hung UK parliament, this the followers of Robinson hope would create enough mutual trust to strive towards a merger. Unionism, under a single party, therefore could harvest further electoral gains in the Assembly as well as Westminster thus strengthening the hand of the pro-Union electorate.

So the paradox of the fall of the House of Paisley could be the bolstering of unionism and the frustration of the republican dream of securing a United Ireland by 2016, the 100th anniversary of the Easter Rising.

This is an update of an earlier post written today by Henry McDonald before the announcement of Paisley's resignation